1. Field of the Invention
This invention relates to integrated sputtering apparatus for use in triode sputtering systems and more particularly to an integrated sputtering means having an ion target of at least one selected material and a controlled magnetic field having substantially linear lines of magnetic flux.
2. Description of the Prior Art
Triode sputtering apparatus, means and systems are well known in the prior art. An integrated sputtering apparatus and method are disclosed in U.S. Pat. No. 4,155,825 which was issued to the inventor of the present invention.
In U.S. Pat. No. 4,155,825, the integrated sputtering apparatus disclosed therein includes a magnetic means which is positioned adjacent the under surface of the ion target for establishing a controlled magnetic field of flux having shaped magnetic lines of force which traverse a predetermined path having at least a 90.degree. or more bend and which establishes a magnetic flux pattern having at least one selected flux density and at least one field direction adjacent to the surface of the ion target. In the embodiment disclosed in U.S. Pat. No. 4,155,825, elongated permanent magnets were positioned on the under side of the target and were utilized for establishing the magnetic field. The strength of the magnetic field was well under 100 gauss with field strengths in the order of 40 gauss being preferred.
The use of a magnetic means for establishing a magnetic field having a strength in the order of less than 100 gauss was important in order to maintain an interrelationship between the magnetic field strength and the cathode potential. This enabled plasma entrapment to be maintained intimately with the upper surface of the ion target.
In known magnetron sputtering sources, a description of which is set forth in detail in U.S. Pat. No. 4,155,825, magnetic field strength in the order of about 100 gauss are utilized, but magnetic field strength more typically in the range of 250 gauss to 1000 gauss are required for efficient source operation.
In magnetron sputtering sources, an interrelationship exists between the magnetic field strength and the cathode potential. The relationship can be represented by the following equation (1) wherein: ##EQU1## (a) .vertline.E (B).vertline. is the absolute value of the electric field which is a function of the B field; and
(b) .vertline.B.vertline. is the absolute value of the magnetic field in gauss
As shown by the above equation (1), plasma entrapment in the magnetron source collapses if the cathode potential E (B) appearing on the cathode, for a fixed weak magnetic field, exceeds a critical value. Similarly, for fixed cathode voltage, if the magnetic field strengths are weakened below a critical level, plasma collapse occurs. Thus, in known magnetron sputtering sources, a balance between minimum magnetic field strength and maximum cathode potential must be maintained in order to achieve stable magnetron source operation.
In the integrated sputtering device disclosed in U.S. Pat. No. 4,155,825, weak magnetic fields with a high cathode potential are utilized. Thus, triode sputtering apparatus utilizing the teachings of U.S. Pat. No. 4,155,825 are free from the inherent relationship limitation between the E field and B field imposed on magnetron sources.
Although triode sputtering apparatus operate with considerably higher gas ionization efficiencies than magnetron sputtering sources, the target current densities which can be obtained from a magnetron source are typically substantially greater than the target current density of a triode sputtering source. There are a number of applications where it would be desirable to have a triode sputtering apparatus which would operate with the higher gas ionization efficiencies of the triode sputtering apparatus disclosed in U.S. Pat. No. 4,155,825, but with higher target current densities which are typical of magnetron sources.